Add the Date chip parsing.

[jbeder]

Also add a formatting option formatISODate (in the UI "Format dates as YYYY-MM-DD"); when enabled, formats date chips as YYYY-MM-DD, and when disabled, formats date chips as they're displayed in the document (see https://developers.google.com/apps-script/reference/document/date#getDisplayText()).

[jbeder]

I shared my copy of the verification document (here, but only you have access, not random passers-by).

This is partial support for #99, which asks for all smart chips (not just dates).

Also, I'm open to suggestions about formatting options. I need ISO format (YYYY-MM-DD) for myself, and I figure a good default is whatever is displayed in the doc.

[evbacher]

Hi Jesse -- thanks for this contribution! I will try to take a look later this week when I have some time for this project.